Multifocal lenses are designed to provide different lens powers, e.g., near vision and distance vision, for a person wearing the lenses. Contact lenses are routinely used by presbyopic patients who can no longer accommodate fully. One approach to the correction of presbyopia is to use simultaneous vision lenses. Compared to bifocal and progressive lenses which require the eye to select, e.g., by shifting upward or downward, different zones of a spectacle lens used to view near or far objects, the simultaneous vision lenses allow the eye to view near or far objects through multiple powers, e.g., both distance and near powers, at the same time across the pupil. That is, the simultaneous vision lenses allow the presbyopic patients to select a correct power choice across the pupil depending on how close or far the objects are.
Meanwhile, in manufacturing custom lenses, systems and methods for designing a lens can be utilized. Methods for calculating image properties are known, and these have been used for both monofocal and multifocal lenses. These can be used to evaluate general properties for a specific design. For a multifocal contact lens design to be customized for an individual patient, however, there is a need to thoroughly evaluate the imaging performance of the individual patient over a number of optical design variables, such as a range of object distances, a range of pupil diameters and the amplitude of accommodation. The clinical consequence of presbyopia may be represented in terms of such design variables. For example, as a person becomes more presbyopic, the person is not able to view an object at a customary working distance without experiencing visual symptoms; an increased pupil size may result in reduction in the range of clear near vision in dim light; and the amplitude of accommodation may be insufficient to meet the near vision demands of the person. Moreover, with presbyopia, the accommodative power of the eye declines over a period of years. Therefore, the presbyopic patients will need different add powers as presbyopia progresses and there is a need for reassessing the lens design periodically.
Many multifocal contact lenses do not correct for the astigmatism of the eye, which can degrade both monofocal and multifocal vision. A customized multifocal contact lens will also have astigmatism corrected, if appropriate.
Therefore, to take the appropriate information and use it to change the lens design for an individual patient, there is a need for identifying design variables that are clinically important for correcting presbyopia and utilizing those design variables to simulate images for both the near vision and distance vision to optimize clinical implementation of custom lenses for the individual patient.
Furthermore, it is recognized that as technology advances, different types of custom lens designs may be developed. Accordingly, there is a need for custom lens design systems and methods that can easily support new types of custom lens designs.